1. Field of the Invention
The present invention relates to electrical connectors and, more particularly, to a socket connector for receiving terminals from a mating component.
2. Brief Description of Earlier Developments
U.S. Pat. No. 5,044,973 discloses an electrical connector for receiving male contacts of an electrical component. The connector has preload pins to preload arms of electrical contacts of the connector in an open position. U.S. Pat. No. 5,704,800 discloses an inner wall projection of a housing used to preload a contact arm.
One of the problems in the design of high pin count connectors is the amount of force that is required to mate the connectors. A minimum amount of normal force (approx. 30 grams per contact) is required for a reliable contact interface for gold plated contacts. Usually most applications limit the total mating forces to less than 10 lb for repetitive operations. This means that there is finite limit, based on the sliding friction alone, to the maximum pin count for a standard connector; around 450 contacts at the minimum normal force. However, this does not take into account the increased friction at the initial part of the contact mating cycle; when the contact is first opened. This additional force approximately doubles the initial forces which further limits the pin count. In other words, even less than 450 contacts will exceed the mating force limit.
Fortunately, there have been developed a number of techniques to allow large numbers of pins to be mated. One of these methods is ZIF, which means that either small or almost no "Z-axis" forces are required to mate the connector. This typically is done in two basic ways. In one case the contacts are "normally open" and are cammed into contact position using an external plate. In other cases the contacts are "normally closed" and they are temporarily cammed open and then closed after insertion of a pin. Both of these designs share the problem of having sufficient contact "wipe.revreaction. to remove films and contaminants. Another method is to use some form of mechanical advantage to drive the pin assembly laterally into a contact, eliminating "Z-axis" forces and having sufficient contact wipe to maintain reliability. Typically, the mechanical advantage of a lever driving the pin assembly can reduce the mating forces to acceptable levels. However, historically these mechanisms have not been easy to design and implement. The designs typically have had problems with flexing and bowing resulting in hystersis in the connector assembly. Recent requirements of higher pin counts (600+ pins) coupled with changes of density from 0.100 centers to 0.050 centers, in addition to requirements for lower mating heights, make these problems even more difficult to solve.